Conventional cache systems track a valid and dirty status for each block (sector) within a cache line. For a 64 KB cache line, 32 bytes of valid and dirty flags are used. Since the amount of cache has grown dramatically since Solid State Devices (SSD) began to be used as caching memory, the amount of memory overhead associated with keeping track of each sector has grown linearly with the number of cache lines.
It would be desirable to reduce the amount of memory needed to keep track of the valid and dirty status and/or allow more memory to be used as actual data cache.